MCE Ph.D. Thesis Seminar

Abstract:
The thesis focused on the characterization of coherent structures and their interactions in a turbulent boundary layer, with application to passive scalar transport and the aero-optic problem. First, connections were identified between instantaneous and statistical descriptions of coherent velocity structures through the study of experimental velocity data of a turbulent boundary layer and an analysis of representative models for energetic turbulent structures. The representative models were used in a novel conditional averaging technique to identify the average behavior of small scales about variations in the large-scale streamwise velocity field in experimental and computational data. Based upon the results of this analysis, a hypothesis for a scale interaction mechanism was proposed involving three-dimensional critical layers. The modeling and analysis methods were then applied to the aero-optic problem in which optical beams are distorted after passing through variable-density turbulent flows. A conditional averaging analysis of simultaneous velocity and aero-optic experimental data identified that the nonlinear interaction of two turbulent scales was most correlated to the aero-optic distortion. The modeling of this interaction using a linear superposition of coherent structure models led to new insights regarding the instantaneous relationship between the velocity and scalar fields over a range of Prandtl numbers.